The present invention is directed to a process for the cationic polymerization of butenes to prepare viscous polybutenes in the number average molecular weight (M.sub.n) range of from about 300 to about 5,000 having enhanced addition reactivity with unsaturated intramolecular anhydrides such as maleic anhydride.
Viscous polybutenes possessing the above described molecular weights have viscosities in the range of about 4 to about 40,000 centistokes at 100.degree. C. Such polybutenes are commercially available from polymerization of refinery butenes, e.g., isobutylene, cis-butene-2 and butene-1 generally present with butane in a C.sub.4 fraction. Commercially since about 1940, such C.sub.4 fractions with or without added isobutylene, or isobutylene rich concentrates typically have been polymerized in the presence of Friedel-Crafts catalysts, such as aluminum halides, ferric halides, zinc halides, boron halides (i.e., BF3), tin halides, mecuric halides, and titanium halides.
The wide range in viscosity and in the molecular weight depends, as is known, on polymerization temperature, catalyst and its concentration, and on the olefin content of the feed.
The viscous polybutenes are essentially water white and thermally decompose with no residue at temperatures above 275.degree. C., and have some use applications in engine oils as anti-scuff agents and viscosity index improvers and in fuels for internal combustion engines to reduce or suppress deposits in the fuel induction system. The viscous polybutenes have also found use as components of caulking compounds, adhesives and electric-cable insulating oils.
However, the greatest use of the viscous polybutenes has been as a raw material in the manufacture of addition agents for lubricating oils, fuels and gasoline, because the viscous polybutenes are reactive olefins and impart a branched-chain alkyl structure to derivatives thereof, enhancing their solubility in petroleum products such as lubricant oils, fuels, and refinery streams.
The derivatives of most interest in the past 15 years are the polybutenyl-substituted saturated intramolecular anhydrides of aliphatic dicarboxylic acids, such as succinic anhydride. The derivatives are synthesized by reacting a polybutene with an unsaturated intramolecular anhydride. Thus, polybutenyl substituted succinic anhydride (also referred to herein as PIBSA) is obtained by reaction of the polybutene with maleic anhydride. The polybutenyl-substituted saturated aliphatic anhydrides have been used per se, or as intermediates in the synthesis of diester amide, imide, amidine, and imidine, addition agents in petroleum products. Such addition agents when derived from polybutenes of 500 to about 5,000 M.sub.n have found extensive use as detergent-dispersants in motor oils and lesser use as carburetor detergents in gasoline, heat exchanger antifoulants in refinery streams, rust and corrosion inhibitors in surface coatings, and as emulsifiers and demulsifiers.
The synthesis of these latter nitrogen containing addition agents, however, proceeds through the carboxyl groups of the anhydride (see for example U.S. Pat. No. 3,131,150). Consequently, in many instances, the usefulness of polybutenes for the synthesis of said addition agents is directly related to the ability of the polybutene to react with the unsaturated anhydride, thereby functionalizing the polybutene with reactive carboxyl groups. Unreacted polybutene by-product associated with the production of the polybutenyl-substituted saturated anhydride is considered inert relative to reactions conducted with, and proceeding through, the carboxyl groups of the polybutenyl-substituted anhydride in the formation of said addition agents.
Accordingly, while such unreacted polybutene does not have to be removed after the polybutenylsubstituted saturated anhydride synthesis, it decreases the amount of active ingredient of the addition agent, on a weight percent basis, ultimately formed from the substituted-anhydride when it is not so removed, thereby requiring more of the mixture of unreacted polybutene and active ingredient to produce a given effect.
As indicated above, a prime utility of the polybutenes discussed herein is as a starting material in the synthesis of polyisobutenyl succinic anhydride (PIBSA) intermediates. There are a variety of methods which can be employed in the synthesis of PIBSA from maleic anhydride and polybutene, said polybutene also being referred to herein as polyisobutylene (PIB) because of the high isobutylene content present therein. Consequently, the following discussion attempts to illustrate the importance of PIB reactivity in the context of these methods.
As is well known in the art, two principle routes exist for the preparation of PIBSA using PIB having the molecular weights (M.sub.n) described herein, namely, a one step method and a two step method.
The one step method involves the direct reaction of maleic anhydride and PIB in a single stage. The one step method can be further subdivided into processes involving the presence of chlorine and those involving the absence of chlorine.
When the one step method is conducted in the absence of chlorine, a mixture of molten maleic anhydride and polyisobutylene is heated to produce PIBSA directly. The resulting product is commonly called thermal-PIBSA or T-PIBSA and is also referred to herein as conventional PIB.
In the alternative one step method, molten maleic anhydride and polyisobutylene are mixed together, gaseous chlorine is added to the mixture, and the mixture heated and reacted to form PIBSA. This method is disclosed in U.S. Pat. No. 3,215,707. The chlorine reacts with the PIB in situ and the chlorinated PIB more readily reacts with maleic anhydride also present in situ, than unchlorinated PIB. This embodiment of the one step method requires approximately equi-molar amounts of maleic anhydride and chlorine in the reaction mixture.
The two step method is conducted by reacting polyisobutylene with chlorine in a first step to produce a chlorinated polymer commonly called chloro-PIB (C1-PIB). The C1-PIB is then reacted with maleic anhydride to form a product known as chloro-PIBSA or C1-PIBSA. This method is described in U.S. Pat. No. 4,234,435.
The chlorinated one and two step methods were developed as a means for achieving higher yields of PIBSA due to the low reactivity of conventional PIB with maleic anhydride in the thermal route. However, the use of chlorine is associated with disadvantages in that chlorine is a toxic gas which produces HCl that must be neutralized with large amounts of caustic before disposal. This increases the cost of the process and necessitates the use of additional equipment to ensure saftey and comply with environmental regulations. The chlorine based processes are advantageous in that the initial reactivity of the PIB with maleic anhydride is not a prime consideration. This stems from the fact that the chlorinated PIB formed in either the appropriate one or two step methods is so much more reactive than conventional PIB that the initial reactivity of the latter becomes essentially irrelevant to the ultimate yield of PIBSA. However, this effect is not achieved without the use of high amounts of chlorine sufficient to permit all the PIB molecules to be chlorinated. It is the very use of high amounts of chlorine, however, which gives rise to the disadvantages of the chlorinated routes to PIBSA.
The initial reactivity of the PIB is extremely important, however, for the formation of thermal PIBSA which does not involve chlorine. Moreover, it is the absence of chlorine which makes the thermal-PIBSA route extremely attractive from an economic and environmental standpoint.
Thus, economics and the current regulatory environment constitute prime motivations for improving the reactivity of polybutenes to enable them to be used more efficiently in the thermal-PIBSA route.
In view of the above, there has been a continuing search for processes which enable the production of polybutenes having enhanced reactivity with said unsaturated intramolecular anhydrides. The present invention was developed as a result of this search.
Enhanced reactivity is imparted to polybutenes in accordance with the present invention by process steps which increase the proportion of reactive double bond types present therein that facilitate the desired reactions sought to be subsequently induced.
More specifically, viscous polybutenes are complex mixtures of polymers, and copolymers of, inter alia, isobutylene, cis-butene-2 and butene-1. The nature and relative amounts of the butene monomers involved in the polymerization leading to a particular M.sub.n polybutene are not indicative of the resulting polymer product because extensive isomerization occurs during polymerization and because of the differences in reactivities of the individual monomers.
The non-olefinic chain portion of the polybutene molecules is composed of normal butyl and isobutyl monomer units and hence is a long branched alkyl chain.
The heavier polybutenes (e.g., 500 to 5,000 M.sub.n) contain a majority of isobutylene units.
As is well known in the art, double bond types can be classified according to the number of hydrocarbon ##STR1## wherein R, R.sup.1, R.sup.2 and R.sup.3 are hydrocarbyl groups.
In polybutene molecules, the disubstituted double bond can be terminal as represented by the formula: ##STR2## or internal as represented by the formula: wherein R and R.sup.1 represent hydrocarbyl groups.
In polybutene molecules, trisubstituted double bonds can be viewed as being terminal with reference to the polymer chain as represented by the formula: ##STR3## or internal as represented by the formula: ##STR4## wherein R and R.sup.1 are as described above, although it is more conventional from the standpoint of nomenclature to treat all trisbustitued double species as internal. Consequently, while one does not normally distinguish trisbustituted double bonds as being internal or terminal strictly on a nomenclature basis, such distinctions are useful because of the difference in reactivity associated with these types of double bonds.
A tetrasubstituted double bond in polybutene molecules can be represented by the formula: ##STR5## wherein R, R.sup.1, R.sup.2, and R.sup.3 are hydrocarbyl groups.
Normally one does not detect the presence of monosubstituted double bonds in polybutene molecules.
Various analytical methods are employed to identify the proportion and nature of the polybutene double bond types. Such analytical methods area subject to certain limitations.
For example, conventional IR analysis is capable of easily distinguishing between disubstituted and trisubstituted double bonds and the proportions of each type in a polybutene sample. However, IR has difficulty by itself in distinguishing between internal and terminal disubstituted double bond types. Conventional IR techniques cannot detect tetrasubstituted double bond types.
The Proton Magnetic Resonance (PMR) analytical technique can provide essentially the same infomation as IR about double bond types, and additionally can distinguish between internal and terminal disubstituted types of double bonds. PMR can provide some information relative to quantifying the amount of internal and terminal disubstituted double bonds based on the principle that signal strength is proportional to the number of magnetic nuclei (See Puskas et al cited and discussed hereinafter). However, PMR is not the method of choice for quantifying the proportion of internal and terminal disubstituted double bonds. PMR cannot detect tetrasubstituted double bond types.
Carbon-13 NMR is the method of choice for quantifying the proportion of internal and terminal disubstituted double bonds. Carbon-13 NMR also can detect and quantify tetrasubstituted double bond types.
If one arranges the double bond types in their order of reactivity, information on the proportion of each double bond type in a polybutene sample in conjunction with the total theoretical unsaturation content allows one to determine the relative reactivity of the polybutene sample based on these proportions.
Thus, with respect to polybutene addition reactivity to maleic anhydride, it is generally accepted that isobutylene double bond types arranged in decreasing order of reactivity are terminal disubstituted, terminal trisubstituted, internal disubstituted, internal trisubstituted, and tetrasubstituted.
Since the terminal disubstituted double bond type is considerably more reactive than the remainder of the other double bond types and the tetrasubstituted double bond type may be considered to be essentially unreactive, the relative proportional distribution of these two double bond types in a polybutene sample permits one to judge whether a particular polybutene sample will be more or less reactive than another sample. The structural analysis method for determining relative reactivity is extremely convenient and allows one to predict reativity without actually having to react the polybutene with unsaturated intramolecular anhydride.
An alternative method for determining the relative propensity of a polybutene sample to react with the unsaturated intramolecular anhydride involves an analysis of the reaction product itself to determine saponification number (Sap. No.) thereof. The Sap. No. is two times the acid number of the sample which is determined by hydrolyzing the anhydride g roups o f the poly-butenyl-substituted intramolecular anhydride to the acid moiety, and the resulting carboxyl groups reacted with KOH. The degree of reaction is then used to calculate the Sap. No.
From the Sap. No., one can mathematically express the moles of unsaturated intramolecular anhydride which reacted as a percent of the total number of moles of said unsaturated anhydride which should have reacted to form the number of moles of polybutenylsubstituted saturated intramolecular anhydride product present in a 1 g. sample of pure product as follows: ##EQU1## wherein R=Reactivity
M.sub.n =Polybutene number average molecular weight as determined by vapor phase osmometry. PA1 A=Mol. wt. of the unsaturated intramolecular anhydride. PA1 56.1=Mol. wt. of KOH. PA1 2=The number of carboxyl functional groups reacted with KOH per anhydride moiety. PA1 1000=Unit conversion. PA1 Sap. No.=In units of mg to g.
When the unsaturated intramolecular is maleic anhydride, the formula of Equation I can be simplified as follows: ##EQU2##
The above Equations I and II make the assumption that no more than one molecule of unsaturated anhydride will react with one molecule of polybutene. Since this assumption does not always hold true, it is possible to obtain a percent reactivity in excess of 100%.
Thus, a higher % R value reflects a higher actual polybutene reactivity subject to the below described caveat.
One caveat in using the formulas of Equations I or II is that relative reactivity of two different polybutene samples cannot be determined by this method unless the polybutenyl-substituted saturated intramolecular anhydride forming process conditions which influence reactivity are held constant from one product to another.
For example, in reactions involving polyisobutylene (PIB) and maleic anhydride (MA) to form PIBSA, it can be established that three process conditions will affect the degree of reaction of a given PIB sample with MA, namely, the PIB:MA mole ratio at which the reaction is conducted as well as the PIBSA forming reaction temperature, and reaction time. Moreover, it can also be established that for a given PIB sample: (a) the higher the amount of MA employed, the higher will be the Sap. No. and the higher the (%R) value; (b) the higher the PIBSA forming reaction temperature and/or pressure, the higher will be the Sap. No. and (%R) value; and (c) the longer the PIBSA forming reaction time, the higher will be the Sap. No. and (%R) value.
For the above reasons, it is considered more convenient to characterize polybutene reactivity on a relative basis using structural analysis since this method is independent of the subsequent reaction conditions which are employed to make the PIB-unsaturated anhydride adduct.
It will be understood that an intrinsically more reactive polybutene when reacted with an intramolecular anhydride to form the corresponding adduct (e.g. PIBSA) will produce less unreacted polybutene in the resulting product. The proportion of resulting adduct and unreacted polybutene in the reaction product mixture can be expressed on a weight % basis as % Active Ingredient (A.I.). Thus, for example, a reaction product derived from PIB and maleic anhydride will typically be composed of PIBSA as the active ingredient and unreacted PIB which is essentially an inert diluent with respect to subsequent addition agent formation. Consequently, a reaction product containing 90% A.I. in this context signifies 90 wt. % of the product will be PIBSA and the remaining 10% inactive and composed primarily of unreacted PIB and any solvent. The % A.I. never exceeds 100%.
The addition reaction between the viscous polybutene and intramolecular anhydride of an unsaturated aliphatic dicarboxylic acid can typically use any one or more of maleic anhydride, citaconic anhydride, itaconic anhydride, ethyl maleic anhydride, sulfonated maleic anhydride, and the like although maleic anhydride is preferred. The addition reactions are, in general, conducted at temperatures in the range of 150.degree. C. to 300.degree. C. using polybutene to anhydride molar ratios of reactants in the range of typically from about 1.0:0.8 to about 1.0:5.0; and preferably from about 1.0:1.05 to about 1.0:1.15.
As indicated above, polybutenes are typically prepared using a Friedel-Crafts type catalyst. Recently, there has been a resurgence of interest in the use of a BF.sub.3 catalyst which has been recognized as producing a more reactive polybutene than for example AlCl.sub.3. This enhanced reactivity has been attributed to an increase in the proportion of terminal disubstituted double bonds induced thereby as described in Nolan et al I, U.S. Pat. No. 3,024,226.
However, it has also been reported that BF.sub.3 favors isomerization of the polybutene double bonds to give polymers with less reactive non-terminal double bonds.
For example, Puskas et al. in The Journal of Polymer Science, Symposium No. 56, pp 191-202 (1976) have reviewed the relative effects of catalysts such as boron trifluoride and complexes thereof with cocatalysts such as acetic acid and water.
They concluded that on a quantative basis, terminal disubstituted (i.e. vinyldiene) double bonds formed initially diminish under the influence of the BF.sub.3 catalyst. This conclusion was drawn from a series of experiments conducted at 5.degree. C. in a batch reactor wherein isobutylene was polymerized with BF.sub.3, BF.sub.3.AcOH and BF.sub.3.H.sub.2 O catalysts. The amount of catalyst employed in each run was never specified. Each experiment was conducted in two stages. In the first stage, the reaction was conducted for 5 to 7 minutes, samples withdrawn, quenched, and analyzed. The reaction was then allowed to proceed for an additional 75 to 90 minutes and samples were again analyzed. (While no quench was disclosed in the above publication to have been performed on the 75 to 90 minute samples, a transcript of the lecture presented by Puskas et al. on June 22, 1976 based on the aforedescribed paper indicates that the 75 to 90 minute sample was quenched after it was allowed to warm up to room temperature.) The results for these runs appear at page 197, Table 1. In Table 1, Polymer A designated the quenched 5 to 7 minute reaction time sample, and Polymer B designated the final polymer sample after 75 to 90 minutes reaction time.
The data of Table 1 show that quantitatively, the overall theoretical unsaturation content of the PIB and the percentage of PIB trisubstituted double bonds, for the runs employing the unpromoted BF.sub.3 catalyst, remained essentially the same for Polymers A and B. However, the total disubstituted double bond content dropped from 30% of the theoretical unsaturation content in Polymer A to 13% in Polymer B. Similar, although less drastic, drops were observed with the promoted catalysts of BF.sub.3.AcOH and BF.sub.3.H.sub.2 O. The drop in disubstituted double bond content was attributed by Puskas et al. to the isomerization of the disubstituted double bonds to tetrasubstituted double bonds.
The criticality of a short reaction time in relation to the use of BF.sub.3 for polymerizing isobutylene is also disclosed in Boerzel et al, U.S. Pat. No. 4,152,499. In this patent, the mean polymerization time is confined to from 1 to 10 minutes in order to suppress undesired double bond isomerization. An optional quenching procedure is disclosed but no benefit is alleged to be associated therewith. The amount of BF.sub.3 employed is characterized as "higher than usual" and varies from 1 to 20 mmoles BF.sub.3 per mole of isobutylene in the feed (i.e. 0.12 to 2.5 wt% of isobutylene in the feed). While short reaction times are employed in this patent to enhance reactivity, such reaction times typically are associated with low isobutylene conversions and polybutene yields.
This problem is recognized and discussed in Child et al., U.S. Pat. No. 3,125,612. In this patent reaction times are confined to the range of 45 to 55 minutes. Thus, it is disclosed that the residence time must be sufficiently long to permit efficient catalyst utilization as measured by monomer conversion and at the same time must not be excessively long to prevent undesirable reactions from occurring.
Thus, on the one hand, enhanced reactivity is disclosed in Boerzel et al. to require polymerization times of from 1 to 10 minutes, and on the other hand, polymerization times of not less than 45 minutes are disclosed in Child et al. to achieve high monomer conversions.
Accordingly, it would be highly desirable to not only achieve enhanced reactivity in the polybutene product but to do so while simultaneously achieving high conversions and high catalyst utilization. BF.sub.3 catalyst is expensive and it would be extremely beneficial to be able to achieve high conversions, impart high reactivity to the polybutene and still not use excessive amounts of catalyst.
U.S. Pat. No. 4,605,808 discloses the cationic polymerization of 1-olefins such as isobutylenes using at least 8, e.g., 8 to 70, preferably 12 to 20, minute contact times with a preformed BF.sub.3 catalyst complex. The preformed catalyst is prepared by reacting BF.sub.3 and a C.sub.1 to C.sub.8 alcohol to form a complex which complex is introduced into the reactor. In Example 1, isobutylene was polymerized for 16 minutes and the reaction terminated by using an excess of 1% acetonitrile in heptane "which was continuously added to the product collection vessels." Thus, while a quenching procedure was employed, the amount of time which elapsed between the exit of the polymer solution from the reactor and the collection of the product is not specified nor is the temperature of the polymer when quenched reported. Moreover, no beneficial effect is disclosed to be associated with quench. As will be discussed hereinafter, the process of the present invention relies on immediate quench of the polymer before the temperature of the same has increased to point at which undesirable side reaction and isomerization occurs.
Webb, U.S. Pat. No. 2,099,090, is directed to the polymerization of isobutylene to make plastic resins of high molecular weight. Based on the discovery that isobutylene polymerization with BF.sub.3 is complete within a "few minutes" at -80.degree. F. (-62.degree. C.), whereas normal butylenes polymerize very slowly (Col. 1, Lines 30 et seq.), a quenching procedure is employed at reaction temperature to stop the reaction before the less reactive olefins have a chance to polymerize when the temperature is allowed to rise. This is said to be contrary to conventional practice wherein the product is allowed to warm up to room temperature and the BF.sub.3 distilled off. While this patent is directed primarily to high molecular weight polymers, the patent discloses that isobutylene polymers having molecular weights of "several hundred up to 10,000 to 15,000" can be produced (Col. 2, Lines 1 et seq.). The highest molecular weight polymers are produced at the lowest temperatures, e.g., -80.degree. to -100.degree. F. Typical reaction temperatures disclosed vary from -80.degree. to -40.degree. F. (i.e. -62.degree. to -40.degree. C.)(Col. 2, Lines 10 et seq.). The BF.sub.3 concentration varies from 0.1 to 0.5% presumably based on the weight of pure isobutylene (Col. 2, Line 16). The specific reaction time illustrated at Col. 3, Line 15 in the example is 10 minutes. Quenching is achieved at reaction temperature with a mixture of ethyl alcohol and water. Thus, polymerization times in excess of 10 minutes are not disclosed nor is the effect of immediate quench on the reactivity of the PIB at reaction times in excess of 10 minutes. The only benefits disclosed to be associated with immediate quench are an increase in SSU viscosity from 242.9 to 245.9 seconds, disappearance of color, and an increase in viscosity index of oil blended with the polybutene.
Quenching is also disclosed in Bannon II, U.S. Pat. No. 2,363,221 at Col. 2, Line 35. However, reaction times are limited to from 0.2 to 0.5 second to produce low molecular weight dimers and trimers of isobutylene. (See also Bannon I, U.S. Pat. No. 2,317,878.)
Hull, U.S. Pat. No. 2,278,445 discloses the polymerization of isobutylene with BF.sub.3 at raaction times of 5 to 30 minutes at catalyst amounts of 0.1 to 2%. No quenching procedure is disclosed and BF.sub.3 is removed from the polymer by vaporization. In addition, non-volatile BF.sub.3 catalyst complexes are eliminated by adding additional isobutylene at temperatures up to 200.degree. F. (93.3.degree. C. )
Russell, U.S. Pat. No. 2,139,038 discloses isobutylene polymerization with BF.sub.3 (0.003 to 1% of feed) using a hydrocarbon diluent, and a reaction time of 1 to 10 minutes. Quenching is employed in Example 1 but the conditions thereof are not specified nor is any benefit disclosed to be associated therewith.
To summarize, none of the aforedescribed art discloses the critical combination of catalyst concentrations, rection time, and immediate quench to produce polybutenes at high conversions having high and/or enhanced reactivity relative to polybutenes prepared at process conditions outside these ranges.